Day et al. U.S. Pat. No. 6,709,744 describes bioactive materials for implantation which include borate-based glass or ceramic materials containing                Na2O—20 to 35 wt %        CaO—20 to 35 wt %        P2O5—0 to 10 wt %        B2O3—30 to 50 wt %A specific example is a glass containing about 22.9 wt % Na2O, about 22.9 wt % CaO, about 5.6 wt % P2O5, and about 48.6 wt % B2O3. These materials contain a high CaO concentration to facilitate the formation of hydroxyapatite when exposed to phosphorus-containing fluids in vivo or prior to implantation. These materials are in the form of loose particulates which are loosely packed, for example in a glass capillary tube for release into a host. Liang et al., Bioactive Borate Glass Scaffold for Bone Tissue Engineering, J. Non-Crystalline Solids 354 (2008), p. 1690-96; and Yao et al., In Vitro Bioactive Characteristics of Borate-Based Glasses with Controllable Degradation Behavior, J. Am. Cer. Soc. 90 (2007), p. 303-306 also disclose borate-based glasses formulated with high CaO to facilitate such formation of hydroxyapatite. For example, the 0B, 1B, 2B, and 3B glasses described by Yao et al. contain 0, 17.7, 35.4, and 53 wt. % borate.        